Pressure responsive motor control circuit for vehicle leveling

ABSTRACT

In preferred form, an automatic vehicle leveling system including a fluid spring component, an electric motor driven compressor and a storage tank. A height controller controls pressure in the fluid spring means in accordance with vehicle load. A diaphragm operated electrical switch is responsive to system pressure to complete a start circuit for the drive motor. It is associated with a solid-state control module and relay hold switch that shunt the pressure switch whereby it opens without arcing. A timer circuit in the module maintains the motor energized whereby the system is pumped down to cause the pressure switch to be pressure biased against operation in response to road movements of the vehicle.

United States Patent Elliott [541 PRESSURE RESPONSIVE MOTOR CONTROL'CIRCUIT FOR VEHICLE LEVELING [72] inventor: James 0. Elliott, Xenia, Ohio [73] Assignee: General Motors Corporation,

Detroit, Mich.

22 Filed: April 9,1971

21 Appl.1\ lo.: 132,713

Related U.S. ApplicationData [62] Division of Ser. No. 816,901, April 17, 1969.

52 U.S.Cl. ..31s/4s1,'31s/487, 307/118, 307/141.4

- s11 moi. ..H02p 1/04 [58] Field of Search ....'..3l8/481, 487; 307/118, 144,

[5 6] References Cited UNITED STATES PATENTS 3,458,772 7/1969, Egart et a1 ..307/141.4 x

1151 3,681,671 [4 1 Aug. 1, 1972 3,048,762. 8/1962 Marsh ..3l8/481X 3,290,576 12/1966 Jensenetal ..3l8/481X Primary Examiner-Benjamin Dobeck I Attorney-W. S. Pettigrew, W. E. Finken and .1. C.

Evans [57] ABSTRACT ln preferred form, an automatic vehicle leveling system including a fluid spring component, an electric motor drivencompressor and a storage tank. A height controller controls pressure in the fluid spring means in accordance with vehicle. load. A diaphragm operated electrical switch is responsive to system pressure to complete a start circuit for the drive motor. It is associated with a solid-state control module and relay hold switch' that shunt the pressure switch whereby it opens without arcing. A timer circuit in the module maintains the motor energized whereby the system is pumped down to cause the pressure switch to be pressure biased against operation in response to road movements of the vehicle.

4 Claims, 6 Drawing Figures PATENTEB AUG 1 1912 3 6 81, 6 7 l sum 1 or 2 I N VEN TOR.

BY James OCW/ofz' gill/W A T TOPNE) PAIENTEDws H912 3.681.671

sum 2 BF 2 I INVENTOR.

A T TORNEY PRESSURE RESPONSIVE MOTOR CONTROL CIRCUIT FOR VEHICLE LEVELING This is a Division of Ser. No. 816,901 filed Apr. 17, 1969. i

This invention relates to automatic vehicle leveling systems and more particularly to such systems having an electrically motor driven compressor controlled to vary pressurization of fluid spring components to maintain a predetermined trim height relationship between the sprung and the unsprung mass of the vehicle.

In order to improve the responsiveness of automatic vehicle leveling systems one approach has been to provide an electrically motor driven compressor that is directly connected to the control chamber of a pressurizable fluid spring to pump down the fluid spring means when a load is removed from the sprung mass so as to return the vehicle to a desired trim height position.

At times the electric motor therein is connected in circuit, relationship with switch means that are mechanically coupledbetween the sprung and the unsprung mass to sense the relative height position therebetween and thereby selectively connect the electric motor in an energization circuit to produce the necessary pump down action. Such arrangements require direct mechanical coupling between sprung and unsprung components and adjustment of the component parts of the coupling to assure desired operation.

In other cases, the operation of the compressor is controlled by a pressure sensitive switch means that is responsive to the pressure level in an exhaust conduit from the fluid spring means, to complete an energization circuit for the motor to effect the desired pump down of the fluid spring means.

One problem with such direct pressure sensing switch means is that means must be included within the switch component to get a snap acting movement of the switch contacts to prevent arcing of the contacts when the switch is connected in a circuit including the load represented by the motor winding. A further problem is that suchswitches require careful calibration and adjustment in order to obtain accurate operation of the system.

An object of the present invention is to improve automatic leveling systems of the type including an elec- I tric motor driven compressor for pumping down fluid spring components of the system by including a pressure sensitive switch for initiating motor operation that is associated with circuit means which isolate the pressure sensitive switch from the load of the motor following initiation of a control cycle of operation.

A further object of the present invention is to provide an improved automatic vehicle leveling system of the type including an electric motor driven compressor for pumping down fluid spring components of the system wherein a control cycle of operation is initiated by a height controller directing exhaust pressure from the fluid spring means against a low cost pressure responsive diaphragm operated start switch and wherein the control cycle of operation is terminated independently of the low cost pressure sensitive switch by means including a hold switch which is associated with time delay means for terminating the control cycle of operation at a point where the pressure switch is subjected to a predetermined pressure level that opens its contacts and prevents operation of the switching components therein in response to vehicle movements.

A further object of the present invention is to improve the reliability and control of anautomatic vehicle leveling system of the type including an electric motor driven compressor to pump down fluid spring components, a leveling system by the provision of means including a low cost oil type pressure start switch that starts a control operation and thereafter is disconnected from the load circuit represented by the electric motor by a hold switch and'wherein means including a three terminal solid state switching device control the hold switch to maintain the motor energized for a predetermined period of time after the start switch opens until the pressure sensitive start switch is subjected to a pressure that prevents it from operating in response to road movement of the vehicle.

These and other objects of the present invention are attained in one working embodiment thereof which includes a pair of combination shock absorber and air spring units that are adapted to be connected between the sprung and unsprung mass of the vehicle. The pressurizable control chambers of the units are interconnected by a cross-over tube and an exhaust conduit runs from one of the control chambers of the inlet fitting of a three position, damped mechanical height controller. An outlet fitting from the controller is connected to the inlet of a switch and delay assembly which includes a low cost oil pressure sensing electrical switch. The pressure switch is a single pole, single throw unit operated by a flexible diaphragm that is directly exposed to an inlet to the switch and delay assembly. The assembly is communicated by a tube to a reciprocating compressor located within the interior of a pressurizable storage tank. A one way check valve component located between inlet and compressor prevents bleed back from thetank to the switch. The compressor has its outlet in direct communication with the interior of the tank and a fluid path is provided through the switch and delay assembly to an inlet fitting of the height controller.

An electrical drive motor for the compressor is electrically connected to'the pressure switch and to a normally'opened relay operated switch. The positive terminal of the vehicle battery is electrically connected to both thepressure switch and the normally opened relay operated switch to control the energization of the motor when the height controller directly communicates the pressure switch with the fluid springs.

The system further includes a circuit board having a semi-conductor switching component thereon and a RC circuit for controlling conductivity of the solidstate switching componen Initially, when the height controller communicates the pressure switch with the air springs the motor is energized to pump down the fluid springs concurrently, the relay operated switch is, conditioned to hold an energization circuit for the motor. This serves to shunt an operating load from the pressure switch.

Following a predetermined pump down period the pressure switch opens and the RC circuit following a delay conditions the semi-conductor switch to cause the relay operated switch to open and thereby de-energize the motor. The final delay phase of the control cycle produces a pressure level within the pressure switch and delay assembly that will bias the pressure start switch against operation in response to ordinary road movements. I

Further objects and advantages of the present invention will be apparent from the following description,

reference being had to the accompanying drawings wherein a preferred embodiment of the present inven tion is clearly shown.

In the drawings:

FIG. 1 is a diagrammatic view of a pump down type automatic leveling system including the control components of the present invention;

FIG. 2 is an electrical circuit diagram of a motor controller for use in the present invention;

FIG. 3 is an enlarged view in vertical section of a pressure switch and delay assembly used in the present invention;

FIG. 4 is a top view of the assembly in FIG. 3 with its cover removed;

FIG. 5 is a side elevational view of the assembly in FIG. 3; and

FIG. 6 is a fragmentary view in vertical section taken along line 6-6 of FIG. 4.

Referring now' to FIG. 1, an automatic leveling system is illustrated of the type including a pair of combination shock absorber and air spring assemblies 10,

12 that are-adapted to be connected between the necessary to point out that the combination assemblies 10, 12 each include a hydraulic double direct acting shock absorber 14 having an outer cylinder 16 with a 1 bottom mount 18 thereon that is adapted to be connected to the unsprung part of a vehicle, for example the rear axle housing of a rear suspension assembly.

The shock absorber further includes a reciprocating piston rod 20 that extends upwardly and outwardly of the cylinder 16. It is secured to an upper mount 22 that is adapted to be connected to a sprung part of a vehicle, for example, the lower frame of the vehicle chassis.

The piston rod 20 also is connected to a top 24 of a cylindrical dustshield 26 that is located in telescoping spaced relationship with the cylinder 16. The dust shield is flxedly connected :to one end of a flexible sleeve 28fby a clamp '30. The sleeve 28 is tumedinwardly of itself and'has the opposite end thereof fixedly secured by a mounting ring 32 to the outer surface of the cylinder'16'.

The outer "cylinder 16, dust shield 26 and flexible sleeve 28 codperateto define a variable volume, pressurizable control chamber 34 in each of the assemblies 10, 12. The combination assemblies 10, 12 thereby are capable of effecting a variable uplifting force on the sprung mass to correct for changes in the static loading thereon.

The above described combination assemblies 10, 12 1 PatsNo. 3,063,701 to Long issued Nov. 13, 1962. It.

'shouldbe understood, however, that other fluid spring means such as elastomeric bellows or bladders located within the primary coil spring of a vehicle between its sprung and the unsprung components and operative to produce a variable uplifting force on the sprung mass to maintain a predetermined relationship between it and the unsprung mass are equally suitable for use with the present invention.

In the illustrated arrangement, the control chambers 34 of the respective assemblies 10, 12 are intercommunicated by a cross tube 36 connected between side couplings 38, 40 on the assemblies l0, 12 respectively.

A second fluid coupling 42 on the dust shield 26 of the assembly 10 is connected to one end of a fluid conduit 44 which has its opposite end connected to a fluid coupling 46 of a three position height controller 48.

The controller 48 is of the type having an outer housing 50 fixedly secured to either the sprung or unsprung mass of the vehicle and further including an oscillatable lever 52 thereon which is pivotally connected to one end of a link 54 that has its opposite end pivotally connected to the other one of the masses. Accordingly, upon relative movement between the sprung and unsprung masses the lever 52 will oscillate so as to move an operating shaft 56 extending from the housing 50 of the controller 48. This will condition valve means (not shown) to first and second and third control positions.

The type of controller 48 is merely representative of one. suitable height controller of the type sensing relative height relationship between the sprung and unsprung masses of a vehicle to control fluid flow within a pressurized automatic leveling system. The controller 48 in particular is of the type set forth in detail in U.S. Pat. No. 2,967,547 to Pribonic issued Jan. 10, 1961.

In the illustrated arrangement it includes an outlet fitting 57 that is connected by a conduit 58 to an inlet port 59 of a pressure switch and delay assembly 60. It has a cover 62 that houses a motor controller 64 for controlling the energization of a DC electric drive motor 66 that operates a reciprocating air compressor 68.

Additionally, the height controller 48 includes an exhaust fitting 69 thereon that is connected by conduit 71 to an outlet port 73 from the assembly 60.

More specifically, in the illustrated arrangement, the drive motor 66 and the reciprocating compressor 68 are located within the interior of a hermetically sealed pressure storage tank .72. The tank includes an upper half 74 joined to a lower half 76 at a continuously formed belt line 78 by suitable fastening means such as resistance welding.

A resilient bump stop 80 prevents the drive motor 66 and the compressor 68 from bumping against the tank 72 because of large amplitude movements therebetween as produced for example by extreme road shock conditions. I

The motor and compressor 66, 68 are resiliently supported in the interior 70 by a suitable spring suspension system representatively illustrated as including a tension spring 82 connected between the joined compressor and drive motor at each corner thereof and the interior surface of the pressure storage tank 72.

The compressor 68 includes an outlet 84 in direct communication with the interior of the tank 70 and it further includes an inlet 86 that is connected by an inlet tube 88 with a port 90 through a base 92 on assembly 60. Base 92 is secured to the tank 72 by weld nut and screw fastener assemblies 93 best shown in FIG. 4. A

gasket 96 seals between cover 62 and base 92 which are connected by screws 97.

The base 92 more particularly includes a large diameter hub 94 directed through an opening 96 in the upper half 74 of the tank 72. An O-ring seal 98 is sealingly located between the hub 94 and the base 92 to seal the opening 96. The interior of cover 62 is vented to atmosphere through vent port 99 in base 92.

The inlet 59 is communicated with the tube 88 through a passageway 100 within base 92. Byvirtue of the above, an inlet fluid flow path is defined from the fitting 46 on' the controller 48 to the compressor inlet 86 by means including the conduit 58, the fitting 59, the passageway 100, thence through. the port 90 and the tube 88 to the inlet 86.

The passageway 100 is closed at its upper end by an enclosure 101 of pressure switch 102 of controller 64. A valve seat 103 in passageway 100 has a valve element 104 spring biased thereagainst by a spring 105 to prevent back-flow of fluid from compressor 68 to the assembly 60. I

Additionally, as best seen in FIG. 5, the system includes an outlet path from the tank interior 70 which includes port 106 to a lateral bore 107 in base 92 which is axially aligned with a side port 108 in the base 92 that in turn is in communication with port 73. The outlet path from the interior 70 is thence completed through conduit 71 and fitting 69 back to the controller 48.

During periods when the sprung and unsprung mass are maintained at a predetermined height relationship therebetween the controller 48 is conditioned by the link 54 and lever 52 so as to cause the valve means therein to assume the first control position, henceforth referred to as neutral to block the conduit 44 from the tank 72 and compressor 68.

When the sprung mass is moved toward the unsprung mass by the addition of static load on the sprung mass the link 54 will cause the lever 52 to oscillate in a direction so as to condition the valve means of the controller 48 into the second control position, henceforth referred to as fill, to open communication between the tank interior 70 and the conduit 44 whereby a precharge of pressure within the tank interior 70 will quickly pass from outlet opening 106 in base 92 thence through port 73 to inflate the control chambers 34 of the assemblies 10, 12 to produce a resultant uplifting action to correct for the increase in static loading so as to return the vehicle to the desired predetermined height relationship where the controller 48 will again block flow to or from the conduit 44.

In accordance with certain principles of the present invention, any static load change that results'in a condition where the sprung mass moves away from the unsprung mass will cause the compressor 68 to be driven by the DC electric motor '66 to pump down the control chambers 34 of the assemblies l0, 12 through the conduit 44.

More particularly, when such a reduction in static loading occurs the controller 48 will be positioned by the link 54 and lever 52 in the third control position, henceforth referred to as exhaust, so as to open communication between the conduit 44 and the inlet 86 to the compressor.

When in its exhaust-position the controller 48 will cause a pressure in the switch 102 corresponding to 6 that of the control chambers 38. This pressure increase acts upon a diaphragm operator 109 in switch 102 through a hollow pedestal base 110 that is threadably seated within the upper end of passageway 100 in the upper face of the base 92.

In addition to the pressure control switch 102, the motor controller '64 further includes a solid-state module or circuit board 114 on one side thereof and a relay operated hold switch 116 that has one terminal thereof electrically connected by a pin conductor 118 to an electrical lead 120 that connects to one end of a run winding 122 of the motor 66. The opposite end of the winding is connected by an electrical lead 124 to group.

In accordance with certain principles of the present invention, the pressure switch 102, the relay operated switch 116 and the solid-state module 114 cooperate to produce a reliable fail safe control of the motor 66 whereby an accurate pump down of the system including control chambers 34 of the assemblies l0, 12 will occur when the height sensing mechanically operated height controller 48 detects a relative height position between the sprung and unsprung mass that corresponds to a reduction in the static loading on the sprung mass to assume its exhaust control position.

The motor controller 64 is more specifically illustrated in the electrical circuit diagram of FIG. 2 including a terminal 126 that is electrically connected by a conductor 128 to the positive terminal of a vehicle battery 130.

This circuit includes a coil energization, motor start network from terminal 126 through a conductor 132 that is electrically connected to a fixed contact 134 of the pressure switch 102. A single pole single throw movable contact 136 of the switch 102 is electrically connected by a conductor 138 to one side of a diode 140. A conductor 142 electrically connects the opposite side of diode to one end of a coil 143 of relay operated switch 116 thence through conductor 145 to a resistor 144 having the opposite end thereof electrically connected by a conductor 146 to ground.

Accordingly, when the pressure switch 102 detects a predetermined cut-in pressure buildup within the pedestal 110 during periods when the controller 48 communicates the control chambers'34 with the switch 102, the diaphragm 109 will flex to close contacts 134, 136 to complete a circuit for energizing coil 143. Hence, in the controller 64 the switch 102 is in effect a start switch for pump down.

Additionally, the controller 64 includes a motor energization hold network for maintaining the run winding 122 energized. More specifically, this circuit runs from the positive terminal of battery 130 through conductor 128, temiinal 126 thence through a conductor 148 to a movable contact carrying blade 150 of the relay operated switch 116. The blade 150 is normally open with respect to a fixed contact 152 that is electricallyconnected by a conductor 154 to the lead line 120 to the run winding 122 and conductor 124 to ground.

When the pressure switch 102 closes, the coil 143 will be energized instantaneously to move an armature 156 in a direction to hold the movable contact carrying arm 150 of switch 116 closed so as to complete an energization hold circuit for the 122.

motor run winding 1 The resistor 144 and the parallel energization circuit to the run winding 122 results in a reduced load on the switch 102 once the relay operated switch 116 is closed. Accordingly, when a predetermined cutout pressure exists in the pedestal 110 and a return spring 158 in the switch housing causes diaphragm 109 to be moved to open contacts 134, 136 the contacts of switch 102 are protected against arcing.

In accordance with certain principles of the present invention, the compressor 68 will pump down the control chambers 34 of the assemblies l0, 12 until the height controller 48 is again returned to a position where it blocks communication between the conduit 44 and the remainder of the closed loop system. Following closure of controller 48, the motor controller 64 is operative to maintain the motor 66 energized for a predetermined delay period until a low pressure condition exists within the pedestal 110 sufficient to maintaina pressure biased opened condition between the movable contact carrying arm 136 and the fixed contact 134 thereof. The bias is caused by atmospheric pressure and spring 158 on the upper face of diaphragm 109 and a below atmospheric pressure on the underside of diaphragm 109. It is of a magnitude that will prevent ordinary road movement forces from causing a premature mating of the movable and fixed contacts of the switch 102 so as to initiate a pump down cycle of operation other than when called for by the height controller 48. p

More particularly, to attain the pressure bias in the illustrated embodiment of the invention, the controller 64 includesa RC charging circuit from battery 130 through conductor 148, switch 116, a resistor 160 connected between sivitch 116 and coil 143, conductor 142, to a capacitor 162. The circuit continues through resistor 164 between capacitor 162 and a conductor 166 to conductor 138. A timing resistor 168 is connected between conductor 138 and a conductor 169 to ground.

When the pressure switch 102 is opened, the control chambers 34 are substantially exhausted by the compressor 68 and the height controller 48 blocks communication between conduit 44 and conduit 58. To pressure bias the switch 102 as mentioned above, the motor energization circuit is maintained for a fixed predetermined delay period following vehicle leveling. The delay is established by the time required to charge the capacitor 162 through the above described circuit.

When a predetermined charge is produced on the capacitor 162 a current pulse occurs in conductor 166 which is connected to the base 170 of a pair of pnp transistors 172, 174. More particularly, the transistors 172, 174 are arranged in an alpha-Darlington configuration drive the emitters of the transistors 172, 174 are connected to one end of the coil 143 and the collectors thereof are connected to the opposite end of the coil 143 whereby the transistor pair 172, 174 is located in shunt relationship thereto.

As a result, when the current pulse in the conductor 166 is imposed onthe base 170, following the time delay established by the above described RC circuit, the transistor pair will be rendered conductive anode terminal 176 to the cathode terminal 178 thereof, through resistor 144 to ground. This causes the coil 143 to be de-energized thereby to cause the switch 116 to open and result in de-energization of the motor 66.

Since the controller 48 is closed the predetermined delay of final pump down results in the volume represented by the conduit 58, port 59, the hollow interior of pedestal 110, passageway 100, port and tube 88 being pumped below atmospheric pressure. This produces a resultant force across the diaphragm 109 that positively maintains separation between the fixed contact 134 and the movable contact carrying arm 136. v

The resultant effect is that the switch 102 is maintained open eventhough it is subjected to substantial jolts, temperature variations or other factors that would conceivably cause a premature mating of the contacts 134, 136 and a resultant premature operation of the compressor drive motor 66. The system is, therefore, rendered fail safe in that is it not operated other than when the controller 48 directly communicates the control chambers 34 with the pressure switch and delay assembly 60.

In the illustrated circuit, diode 140 is included to prevent charging of the capacitor 162 until the relay switch 116 is closed and pressure switch 102 is opened.

The resistor 144 will maintain the transistors 172, 174 conductive after the initial base current pulse to avoid relay chatter at contacts 150, 152.

The system is operated during fill so as to efiect an instantaneous pressurization of the fluid springs when static loading is added to the vehicle. Furthermore, the compressor inlet is precharged by the pressure in the fluid springs during the exhaust phase of operation and the supercharge again reduces the time required to pump down the fluid springs to return the vehicle to a level attitude when static loading has been removed therefrom.

In one working embodiment of the system which was incorporated on a 1967 model Cadillac with a standard suspension vehicle loads of 1100-1200 pounds were corrected with 15 seconds. On the removal of a maximum load following leveling, the aforedescribed system resulted in a return to a desired trim height relationship between the sprung and the unsprung mass within a period of time of from 1 to l rminutes during which time compressor motor 66 was energized so as to cause the compressor 68 to produce pump down.

To effect the aforementioned correction within the time limits set forth the working embodiment of the invention included the following electrical and mechani-' cal characteristics.

Components Compressor 68 Ratings .077 cubic inch displacement drive motor 66 7.8 amps 0 12 volts tank 72 120 180 p.s.i.g. assemblies 10, 12 i0 l20p.s.i.g.

switch 102 l8 p.s.i.g. cut-in and cutout battery 12 volts diode .5 amps at 50 volts coil 143 50 ohms resistor 144 10 ohms 'fi watt resistor capacitor 162 47 ohms 2 watts 100 mfd 25 volts resistor 164 l kohms Va watt resistor 168 120 kohms A watt transistor 178 Motorola MP8 6523 itiates and terminates the operation of the compressor 66 through means including a common three terminal semi-conductor switching device. Furthermore, the motor control configuration has a relay operated hold switch for maintaining the motor energization circuit during most of the pump down phase of operation.

By virtue of the aforedescribed controller 64, the system can be accurately calibrated for a predetermined type of operation without the need for adjusting and carefully calibrating component parts of a mechanical switch. Rather, in accordance with certain principles of the present invention a solid state timer controlled network of the type that only requires adjustment of RC circuit components is included to produce exact points of operation in the system whereby fluid spring components therein can be quickly and accurately pumped down to return the vehicle to a predetermined desired level attitude when static load is removed therefrom.

While the embodiments of the present invention, as herein disclosed, constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A pressure responsive motor control circuit comprising: means including a relay operated switch for energizing an electric motor, said relay operated switch having a coil, means including a pressure responsive start switch for connecting said coil to a power source to energize said motor, said pressure responsive switch responsive to a first pressure to start the motor and responsive to a reduced pressure to initiate a time delayed stop of the motor, means including a resistor and said relay operated switch to hold said coil energized following motor start and while the pressure switch senses the reduced pressure, normally open switch means shunting said coil, timer means responsive to said pressure responsive start switch to condition said normally open switch means to shunt said coil and open said relay operated switch to de-energize said motor a predetermined period after said pressure responsive start switch disconnects said coil from the power source.

2. In the combination of claim I normally open switch means including-a three terminal solid-state device having its anode, cathode terminals connected in shunt relationship to'the coil of said relay operated switch, a terminal on said device responsive to a predetermined control signal pulse to cause said device to be conductive between the anodeand cathode terminals so as to shunt said relay switch coil and thereby open said first circuit means to de-energize said electric motor, said timer means including a resistance, capacitor circuit with a predetermined time delay before said signal pulse occurs on said terminal.

3. A pressure responsive motor control circuit comprising: means including a relay operated switch for energizing an electric motor, said relay operated switch having a coil, means including a pressure responsive start switch for connecting said coil to a power source to condition said relay switch to energize said motor, said pressure responsive switch having a pair of contacts and a diaphragm for moving one of said contacts to a closed and opened position, means for directing a first pressure to said diaphragm to move said contacts closed to start the motor, means including said diaphragm responding to a reduced pressure in said conduit means to open said contacts, means including a compressor operated by said motor to pump down said conduit means to a pressure less than the reduced pressure to cause said diaphragm to be biased in a direction to further separate said contacts against closure, means including a resistor and said relay operated switch to hold said coil energized following motor start and when said pressure responsive switch senses said reduced pressure, normally open switch means shunting said coil, timer means operable when said pressure responsive start switch senses said reduced pressure to initiate a delay period following which said normally open switch means is conditioned to shunt said coil and open said relay operated switch to bypass said holding circuit means and to open said energization circuit means thereby to de-energize said motor a predetermined period after said pressure responsive start switch senses said reduced pressure.

4. In the combination of claim 3, said normally open switch means including a three terminal solid-state device having its anode, cathode terminals connected in shunt relationship to the coil of said relay operated switch, said timer means including a resistance and capacitor circuit charged for a predetermined time delay when said pressure switch senses reduced pressure to produce a signal pulse following the time delay, a terminal on said device responsive to said signal pulse from said timer means to cause said device to be conductive between the anode and cathode terminals so as to shunt said relay switch coil and thereby cause it to be conditioned to open said first circuit means to de-energize said electric motor. I

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,681,671 D d August 1, 1972 Inventor(s) James Ellic'tt.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as, shown below:

In the grant (only) insert the attached columns 5, 6, 7 and Signed and sealed this 1st day of May 1973.

(SEAL) Attest:

EDWARD M.PLETCHER,JR. ROBERT GOTTSCHALK Atte sting Officer Commissioner of Patents F ORM PO-105O (10-69) uscoMM-D 60378-P69 7 U.. GOVERNMENT PRINTING OFFICE: I969 0-35633, 

1. A pressure responsive motor control circuit comprising: means including a relay operated switch for energizing an electric motor, said relay operated switch having a coil, means including a pressure responsive start switch for connecting said coil to a power source to energize said motor, said pressure responsive switch responsive to a first pressure to start the motor and responsive to a reduced pressure to initiate a time delayed stop of the motor, means including a resistor and said relay operated switch to hold said coil energized following motor start and while the pressure switch senses the reduced pressure, normally open switch means shunting said coil, timer means responsive to said pressure responsive start switch to condition said normally open switch means to shunt said coil and open said relay operated switch to de-energize said motor a predetermined period after said pressure responsive start switch disconnects said coil from the power source.
 2. In the combination of claim 1 normally open switch means including a three terminal solid-state device having its anode, cathode terminals connected in shunt relationship to the coil of said relay operated switch, a terminal on said device responsive to a predetermined control signal pulse to cause said device to be conductive between the anode and cathode terminals so as to shunt said relay switch coil and thereby open said first circuit means to de-energize said electric motor, said timer means including a resistance, capacitor circuit with a predetermined time delay before said signal pulse occurs on said terminal.
 3. A pressure responsive motor control circuit comprising: means including a relay operated switch for energizing an electric motor, said relay operated switch having a coil, means including a pressure responsive start switch for connecting said coil to a power source to condition said relay switch to energize said motor, said pressure responsive switch having a pair of contacts and a diaphragm for moving one of said contacts to a closed and opened position, means for directing a first pressure to said diaphragm to move said contacts closed to start the motor, means including said diaphragm responding to a reduced pressure in said conduit means to open said contacts, means including a compressor operated by said motor to pump down said conduit means to a pressure less than the reduced pressure to cause said diaphragm to be biased in a direction to further separate said contacts against closure, means including a resistor and said relay operated switch to hold said coil energized following motor start and when said pressure responsive switch senses said reduced pressure, normally open switch means shunting said coil, timer means operable when said pressure responsive start switch senses said reduced pressure to initiate a delay period following which said normally open switch means is conditioned to shunt said coil and open said relay operated switch to bypass said holding circuit means and to opeN said energization circuit means thereby to de-energize said motor a predetermined period after said pressure responsive start switch senses said reduced pressure.
 4. In the combination of claim 3, said normally open switch means including a three terminal solid-state device having its anode, cathode terminals connected in shunt relationship to the coil of said relay operated switch, said timer means including a resistance and capacitor circuit charged for a predetermined time delay when said pressure switch senses reduced pressure to produce a signal pulse following the time delay, a terminal on said device responsive to said signal pulse from said timer means to cause said device to be conductive between the anode and cathode terminals so as to shunt said relay switch coil and thereby cause it to be conditioned to open said first circuit means to de-energize said electric motor. 